Liquid ink printers having at least one print head from which droplets of ink are directed towards a recording sheet are well known. The print head in some liquid ink jet printers may contain an internal reservoir of ink as is known in ink jet printers. Other liquid ink printers, known generally as phase change ink printers, may be loaded with solid ink sticks that are delivered to a melter, which heats the solid ink stick to its melting point to produce liquid ink. The melted ink may then be collected in one or more reservoirs and distributed to one or more print heads. Within a print head of a liquid ink printer, ink is drawn into a plurality of channels. Power pulses to ink ejection components, such as piezoelectric ejection components, expel droplets of ink from orifices or nozzles of the print head.
A liquid ink print head may be incorporated into a printer that ejects ink onto a media sheet or a media web. A media sheet printer typically includes a supply drawer that houses a stack of media sheets. A feeder removes a sheet or media from the supply and delivers it into a feed path that directs the sheet past a print head so the print head ejects ink directly onto the sheet. In other types of sheet printers, a media sheet in the feed path is pressed into contact with a rotating intermediate member that bears ink, which has been ejected onto the member by one or more print heads.
Another type of printer is a web printer. In a web printer, a continuous supply of media, typically provided in a media roll, is mounted onto rollers that are driven by motors. A loose end of the media web is passed through a print zone opposite the print head or heads of the printer. Beyond the print zone, the media web is gripped and pulled by mechanical structures so a portion of the media web continuously moves through the print zone. Tension bars or rollers are placed in the feed path of the moving web to remove slack from the web so it remains taut without breaking.
One important aspect of these ink printing machines is the stability of the media sheet or web as it passes in front of a print head, which is ejecting ink onto the media. To improve stability of media passing in front of a print head, some printers incorporate a vacuum source that is coupled to vacuum platen. The vacuum platen includes a plurality of passageways or ports to enable air to be drawn through the platen towards the vacuum source. The vacuum platen is positioned and oriented so it is adjacent the back side of the media being printed by a print head. Thus, the air being pulled through the platen pushes the media against the platen to help stabilize the media while it is being printed.
In some known liquid ink printers that use a vacuum source and platen to help stabilize media being printed, an escort belt is also used to move the media along its feed path. An escort belt is typically provided with apertures. The escort belt is configured so it moves over the platen between the media sheet or web and the platen. The apertures in the belt enable air to be drawn through the belt and the passageways of the platen towards the vacuum source. The belt may be treated with friction-reducing material so the belt slides over the platen as it is pulled towards the platen. The escort belt improves the stability of the sheet or web media because it is flexible and its tautness may be adjusted by tension bars or roller.
While media transport systems using vacuum sources with platens and moving escort belts provide improved media stability during printing, an issue regarding debris in the vicinity of the print heads has been observed. Specifically, the airflow that pushes the media against the belt and platen may also displace debris from the media, especially when the media is fibrous, as is the case with paper. Debris displaced in the vicinity of the print head may clog an orifice or otherwise interfere with the ejection of ink onto the media. Reduction of displaced debris in the vicinity of the print head is therefore desirable in sheet printing and web printing machines.
In web printing machines, registration of the web media in the print zone opposite the print heads is important. While an escort belt and vacuum platen help properly maintain registration of the web media in the print zone, the air flow through the belt and the platen carries particulate debris. This debris may accumulate in the vacuum platen and eventually clog some of the passageways in the platen. Removal of this debris from the print zone without clogging the vacuum platen would be useful.